1. Field of the Invention
The present invention relates to a surface-finished stainless steel sheet used for a case and parts of a semiconductor manufacturing device, onto which it is difficult for fine dust to attach and, even if fine dust attaches onto the surface of the stainless steel sheet, the fine dust can be easily removed by cleaning.
2. Description of the Related Art
When the parts of a semiconductor manufacturing device are made, a stainless steel sheet, the surface of which is finished to grade 2B stipulated by JIS, or a stainless steel sheet, the surface of which is polished, has been commonly used.
Conventionally, the stainless steel sheet, the surface of which is finished to grade 2B stipulated by JIS, is manufactured as follows. A cold-rolled stainless steel sheet is annealed and descaled by a continuous heat-treating and acid-cleaning line. After that, the stainless steel sheet is rolled by a skinpass rolling mill so that the material can be adjusted and the profile can be reformed. A surface-polished stainless steel sheet is manufactured as follows. Usually, a stainless steel sheet, the surface of which has already been finished to grade 2B, is used, and it is made to come into contact with a polishing face of a polishing belt or a polishing disk which are being rotated.
However, when a stainless steel sheet, the surface of which is finished to grade 2B, or the surface-polished stainless steel sheet, is used for making the parts of a semiconductor manufacturing device, the following problems may be encountered. Fine dust floating in air tends to attach onto the surface of the stainless steel sheet, and further it is difficult to remove the attached fine dust by wiping and cleaning. Therefore, the manufacturing yield is deteriorated in the manufacturing process by the thus attached fine dust. The reason why fine dust attaches onto the surface of the stainless steel sheet, the surface of which is finished to grade 2B, or the surface of the surface-polished stainless steel sheet is that small dents are formed on the surface, the diameters of which are 0.1 to 0.9 mm, which cause no problems in the case of manufacturing building materials or kitchen devices to which the stainless steel sheet is conventionally applied. The above small dents will be referred to as pinholes, hereinafter.
It is assumed that these pinholes are created and remain on the surface of the stainless steel sheet as follows.
(1) When the stainless steel sheet, the surface of which is finished to grade 2B, is manufactured by the aforementioned manufacturing method, in the continuous annealing and acid-cleaning line in which the cold-rolled steel sheet is continuously annealed and acid-cleaned, the stainless steel strip comes into contact with support rollers for supporting and carrying the stainless steel strip of high temperature in the heat-treatment furnace. Therefore, foreign objects (buildup) attaching onto the support rollers create small dents when the foreign objects are pushed into the surface of the stainless steel strip.
(2) After the continuous annealing and acid-cleaning has been completed, the stainless steel strip is rolled by a skinpass rolling mill so that the material can be adjusted and the profile can be reformed. In the process of skinpass rolling, the rolling is conventionally conducted under the condition of no lubricant, because it is necessary to keep the surface brightness of the stainless steel strip. Therefore, foreign objects attaching onto the work roller or foreign objects carried on the surface of the stainless steel strip create small dents on the surface of the stainless steel strip when the stainless steel strip comes into contact with the work rollers of the skinpass rolling mill.
(3) Further, when the polished stainless steel sheet is manufactured, the stainless steel sheet, the surface of which is finished to grade 2B, is polished as described above. In this case, the surface roughness is suppressed to be #100 to #400 from the viewpoint of ensuring the cleaning property. Therefore, the polishing allowance to be removed by polishing is small. Accordingly, pinholes created in the process of continuous annealing and acid-cleaning and also in the process of skinpass rolling cannot be removed by polishing so that they remain on the surface of the stainless steel strip.
In order to prevent the creation of these pinholes, for example, as disclosed by JP-A-3-207807 and JP-A-3-226517, there is proposed a method of solving the problems of buildup on the support roller in the continuous annealing furnace, by which the surface of the support roller is coated by cermet by means of flame coating so that the resistance to buildup on the surface of the support roller can be improved. However, the above method of coating the surface with cermet is very high expensive, which raise the production cost, and further it is difficult to keep the roller surface uniform and furthermore it is difficult to extend the life of the roller.
Concerning the method of removing the buildup on the work roller of the skinpass rolling mill, there is proposed a brush type roller cleaner for removing the foreign objects attaching on the work roller surface, and further there is proposed a vacuum cleaner in order to remove the foreign object which have been carried being attached onto the surface of the stainless steel strip. However, even if the above methods are adopted, it is difficult to effectively remove the foreign objects creating pinholes, the diameters of which are 0.1 to 0.9 mm, which cause problems in the manufacturing process of a semiconductor device.